Simpson mentioned Civil War: A Nation Divided, which seems only marginally more historical. The subject doesn’t really lend itself well to that game format. CW soldiers didn’t generally run across the landscape like ninjas, using scoped repeating rifles to tote up headshots.

There is a CW mod for Napoleon: Total War, but it’s not a FPS. I am familiar with the game system, but not this particular mod. The underlying game system is solid, but the “vanilla” games as they come commercially are usually pretty awful n terms of historical research. Modifications (or “mods”) like these are built be teams of players and greatly enhance the historicity of the game, but they’re tricky to install and use sometimes.

UPDATE: The mod shown above, “North & South,” appears not yet to be released. There is another, “Blue & Grey,” by the same team; this one seems to be a refinement of that earlier version.

You could probably make a stealth/sniper game out of the work of sharpshooters. Start the game off in the trenches of Petersburg, then have a set of stealth missions leading up the the final big boss — sneaking into Richmond to assassinate Jefferson Davis. Hmmm … I think that could be a pretty good game.